1. Field of the Invention
The present invention relates to an imaging device equipped with an imaging sensor.
2. Description of the Related Art
Dark current components that are superimposed on pixel signals of an imaging sensor equipped in an electronic camera are corrected by a signal processing circuit in the electronic camera. So far, many types of correcting methods have been proposed Japanese Unexamined Patent Application Publication No. Hei 7-236093, and so forth).
However, the conventional correcting methods are based on the assumption that dark current components of each pixel outputs of an imaging sensor are almost constant. Thus, dark current components caused by an FDA cannot be corrected reliably.
Here, the FDA is an abbreviation of Floating Diffusion Amplifier that is disposed at an output end of an imaging sensor.
To cause the FDA to operate, it is necessary to apply a bias current thereto. However, when a current is applied to the FDA, it generates heat.
When the FDA generates heat and in particular electric charge accumulation time is long (30 seconds or longer), dark current components that are ignorable are superimposed on the pixel signals of the imaging sensor.
However, since heat radially spreads from the FDA, the amounts of the dark currents differ depend on the positions of the pixels. Therefore, the dark current components that occur in the imaging sensor caused by the FDA are local.
The dark current components that locally occur cannot be corrected reliably by the conventional correcting methods.
To decrease the dark current components that locally occur, a technology for temporally suppressing the bias current to be applied to the FDA in the case where the electric charge accumulation time of the imaging sensor is long has been proposed. However, since the technology is incapable of completely suppressing heat generation, it is not sufficient to reliably correct dark current components.